The invention concerns a process for tempering preforms made of a thermoplastic material, where the preforms are intended to be blow-molded into containers and where the preform is provided with a temperature profile along a circumference, which is generated by differentially heating strip-shaped portions, which extend in the direction of a longitudinal axis of the preform, and where step-by-step tempering for the purpose of sequential thermal conditioning of different regions of the preform is implemented, and where step-by-step rotation with a motion phase and a rest phase is carried out as well.
The invention further concerns a device for tempering preforms made of a thermoplastic material, which includes at least one transport path for the preforms and at least one heating device, and which provides the preforms with a temperature profile in the circumferential direction and with at least one rotational drive unit for carrying out a rotational movement of the preform, which generates a step-by-step rotational motion of the preforms.
Such a process is used, for example, when containers are to be produced whose cross-sections deviate from a circular shape. The deviation can, for example, consists of producing containers with an oval cross-section or, for example, with a triangular or a rectangular cross-section.
The production of such non-rounded containers was already described in U.S. Pat. No. 3,775,524. At first, a symmetrical tempering of the preforms occurs, then the temperature in selected regions is selectively increased. Further variants of temperature profiling of the preform in a circumferential direction are also described in U.S. Pat. No. 3,632,713, U.S. Pat. No. 3,950,459 as well as in U.S. Pat. No. 3,892,830. A temperature conditioning process by selective shading is presented in DE-OS 33 14 106.
From U.S. Pat. No. 5,292,243 it is known to simultaneously subject two preforms to temperature conditioning in the circumferential direction. In EP-OS 0 620 099 a compilation of processes for temperature conditioning known from the state of the art can be found. A step-by-step rotary motion of the preforms during temperature conditioning is explained in PCT-WO 97 32 713.
The previously known individual processes have a number of disadvantages, for example, a relatively high apparatus cost is incurred, only a relatively poor reproducibility can be ensured, or, according to the device of the last-mentioned publication, the production volume per unit time is limited.
It is, therefore, the objective of the present invention to present a process of the kind mentioned in the introduction in such a manner that a high-quality temperature conditioning process can be achieved at a high rate of production.
This objective is achieved according to the invention in that the preform is transported by a carrier device through a tempering zone, that the carrier device is given a rotary motion by engaging a gear for the initiation of rotary motion, which engages a matching gear and that the preform is moved at least along a portion of the transport path before the gear engages the matching gear, and is moved at least along a further portion of the transport path through the tempering zone after the interaction between the gear teeth has stopped without motion relative to the rotational direction
It is a further objective of the present invention to design a device of the previously mentioned type in such a manner that a selective tempering of the preform can be achieved at a high rate of reproducibility and a high rate of production.
This objective is achieved according to the invention in that a carrier device for the preforms includes a control element, which is disposed eccentrically relative to a longitudinal axis of the carrier device, which can be positioned by a radial cam and which provides positioning of the preform in the direction of rotation, and that the radial cam has at least two cam segments along the transport path, which are parallel to the transport path, as well as at least two cam segments, which are transverse to the transport path.
The step-by-step tempering of a preform makes it possible, for example, to dispose common radiant heaters according to the state of the art along with IR-radiators along a transport path-of the preform and to expose different regions of the preform to the radiation for different periods of time. In this case in particular no costly coordination between the velocity of a longitudinal movement in the transport direction and the speed of rotation is required.
The arrangement of the preform on a carrier device during the heating process makes it possible to allow the forces for carrying out the positional changes and for generating the transport velocity to only indirectly affect the preform. The preform can be disposed at leisure relative to the carrier device, and all movements are generated by the interaction of functional elements with the carrier device. This facilitates a protective handling of the preform, which has been plasticized by the tempering process. By generating the rotary motion in accordance with the process according to the invention by means of the interaction of a gear with a matching gear, a very high flexibility in the setting of the motion sequences is achieved. Moving the preform through sequential phases of a gear engagement and the translational phases of the preform without rotary movements supports the generation of the required temperature profile in the circumferential direction.
The radial cam contemplated according to the device of the invention for positioning the carrier device, facilitates the implementation of position changes of the preform in the direction of rotation without any active actuating elements, but merely by tracking the radial cam during the implementation of the forward motion of the preform. The use of radial cams and associated control elements at the carrier device leads to an exact reproducibility of the rotational positioning actions and avoids deviations from the required positioning which increase along the transport path.
In order to support a space-saving process implementation it is proposed that the preform be transported along a curved heating path.
A simple transport process in the region of the heating device can be achieved by having the preform transported in the region of the heating device by a heating wheel.
For providing a thermal basic conditioning it is proposed that the preform, in an initial region of the heating path, be at first continuously rotated for providing it with a basic tempering.
A further possibility for carrying out a part of the rotary movement consists in positioning the carrier device in a guide rail in the rotational direction by the action of a control element.
An effective initiation of positioning forces can be accomplished by introducing lever-like positioning forces by means of the control element into the carrier device.
A mechanical establishment of a given rotational positioning is supported in that the carrier device, along at least a portion of the transport path, is moved by means of a transversely forwardly oriented lever-like control element.
It also proves to be advantageous that the carrier device is moved along at least a portion of the transport path by means of a transversely rearwardly oriented lever-like control element.
To facilitate a tempering of the wall regions, which are relatively uniform with respect to each other, it is proposed that when the gear teeth engages the matching gear, as well as during an interaction between the control element and the guide rail, a common rotational direction of the carrier device be maintained.
However, alternatively it is also possible that the carrier device, when the gear engages the matching gear, be rotated in the opposite direction to that of an interaction between the control element and the guide rail.
The rotational positioning actions can be achieved at a low degree of friction by providing the control element with a cam roller.
In order to facilitate a modular implementation of the heating device it is proposed that the heating device include heating boxes, which are equipped with infrared radiators.
A spatially effective arrangement of the individual components consists in placing the matching gear between two heating boxes.
In order to achieve an optimum utilization of the available space it is proposed that the heating boxes be placed relative to the transport path of the preforms at the outside along the heating wheel.
An advantageous realization of the carrier device consists in designing the carrier device as a transport rod, which includes a holding device for the preforms.
In order to provide rotational positioning of the preforms as well as of the blow-molded bottles, which is always spatially exact, it is proposed that at least along a portion of the transport path of the preforms outside the region of the heating devices, a radial cam for the control elements be provided.
A further variant for handling the preforms consists in providing radial cams for the control elements, except for the transport path of the preforms through the blow-molding device as well as in the region of a uniform rotation of the preforms along the heating device and along other regions of the transport path of the preforms through the device for blow-molding.